There is disclosed in sales leaflet No. D 310 608/2 C 5.82/N Ku of the Original Hanau division of Heraeus GmbH, a German company, a light and weather resistance testing apparatus equipped with an ultraviolet radiation measuring device. This apparatus includes a sensor which is disposed in the plane of the samples and moves with them, a watertight housing with an optical system, a radiation receptor, an integrator, a memory and a power supply consisting of two 9 V batteries. The radiation receptor permits wavelength measurements in the range from 300 to 400 nm (nanometers). When the rotation of the samples is stopped, the sensor is connected by means of a cable to a read-out apparatus external to the weathering chamber. This read-out device then permits the display of the instantaneous values of the irradiance or momentary radiation intensity (milli-watts/sq. cm) and irradiance or radiation dose (in watt-seconds/sq. cm).